Now, nature is striking back.

A mysterious disease in the last several years has almost made Japan's pearl oysters an endangered species. Unless a solution is found soon, Japan's venerable pearl industry fell it may die soon.

``If the oysters die en masse again this year, most of us will be forced to quit,'' said Toru Nishii, a pearl grower who has been in the business for more than 40 years adding, ``I'm afraid the entire industry will go belly up.'' The die-off is causing some shortages on the world market and prices are rising, people in the American gem trade report. Devin Macnow, executive director of the Cultured Pearl Information Centre, a trade group in New York, expects the shortage to push prices up by ten per cent to 15 per cent this year.

Elizabeth Parker, an appraiser for Curt ParkerJewellers in St Louis, offered a similar prediction, but feels that it is just the beginning considering the given situation. ``I was very pleased with the prices. They are not as high as I expected,'' she said at a jewellery trade show in June.Although the bigger and more expensive south sea pearls from Australia and Tahiti are gaining ground, Japan's Akoya cultured pearls still dominate much of the world market including nearly 65 per cent of sales in the United States.

But just keeping the Akoyas in the market has become increasingly difficult. In 1996, only 56.6 tons of pearls were harvested in Japan, down 22 per cent from the amount harvested in 1993, the year before the first widespread oyster deaths were reported. Those deaths were caused by a red tide - a deadly plankton called heterocapsa.

However, what is killing the oysters now is unknown but, it is undeniably deadly. The mortality rate surged to more than 50 per cent last year, much higher than the average 20 per cent to 35 per cent, accordingto fishery agency statistics. Of the deaths, about 92 million or nearly 55 per cent were first - and second-year pearl-bearing oysters.

Some marine biologists suspect viruses, but their findings have been met with scepticism.

``We haven't been able to isolate any virus, at least at our labs here,'' said Dr Toshihiko Matsusato, a pathologist at the National Research Institute of Aquaculture. ``It could be something totally unknown,'' he said. A government-led team recently speculated the culprit might be a shell-fish parasite called perkinsus, which devastated oysters in the Mississippi river delta nearly 50 years ago.

Since Kokichi Mikimoto, founder of Japan's top pearl company, Mikimoto and Co, started the industry 105 years ago by learning how to induce oysters to grow pearls, technological improvements have made the process relatively easy and amazingly exact. Even a tint of pink or extra glow can be added to harvested pearls.

But some pearl growers suspect artificial insemination and otherscientific tinkering may have inadvertently spawned oysters that are more prone to disease.

``Decades ago, growing pearls was a lot of work and oysters seemed healthier and happier then. But today, the environment is terrible,'' '' said Grower Nishii.